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Seems we are missing C++20 compatibility warning of using deduced type
(e.g. some template class) as a non-type template parameter. Before this
patch the following code crashes clang.
template<class>
struct DC {};
template<DC s> // using deduced type, but considered as "auto" type
auto test() {}
It triggered warn_cxx14_compat_template_nontype_parm_auto_type. However
there is no such "auto" type at all.
Using deduced type within non-type template parameter was introduced in
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0732r2.pdf.
This patch create a new compatibility diagnostic message for this.
Fixes: https://github.com/llvm/llvm-project/issues/57643
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D133609
Files:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaTemplate.cpp
clang/test/SemaCXX/template-nontype-args-compat.cpp
Index: clang/test/SemaCXX/template-nontype-args-compat.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/template-nontype-args-compat.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -fsyntax-only -Wpre-c++20-compat -std=c++20 -verify=cpp20
%s
+
+namespace DeducedClass {
+template<class>
+struct DC {};
+
+template<DC s> // cpp20-warning{{non-type template parameters declared with
'DC' are incompatible with C++ standards before C++20}}
+auto test() {}
+} // namespace DeducedClass
Index: clang/lib/Sema/SemaTemplate.cpp
===================================================================
--- clang/lib/Sema/SemaTemplate.cpp
+++ clang/lib/Sema/SemaTemplate.cpp
@@ -1532,9 +1532,17 @@
CheckValidDeclSpecifiers();
if (TInfo->getType()->isUndeducedType()) {
- Diag(D.getIdentifierLoc(),
- diag::warn_cxx14_compat_template_nontype_parm_auto_type)
- << QualType(TInfo->getType()->getContainedAutoType(), 0);
+ if (TInfo->getType()->getContainedAutoType()) {
+ // template<auto xx>
+ Diag(D.getIdentifierLoc(),
+ diag::warn_cxx14_compat_template_nontype_parm_auto_type)
+ << QualType(TInfo->getType()->getContainedAutoType(), 0);
+ } else {
+ // template<DeducedClass dc>
+ Diag(D.getIdentifierLoc(),
+ diag::warn_cxx17_compat_template_nontype_parm_deduced_class)
+ << TInfo->getType();
+ }
}
assert(S->isTemplateParamScope() &&
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -4833,6 +4833,10 @@
"non-type template parameter of type %0 is incompatible with "
"C++ standards before C++20">,
DefaultIgnore, InGroup<CXXPre20Compat>;
+def warn_cxx17_compat_template_nontype_parm_deduced_class : Warning<
+ "non-type template parameters declared with %0 are incompatible with C++ "
+ "standards before C++20">,
+ DefaultIgnore, InGroup<CXXPre20Compat>;
def warn_cxx14_compat_template_nontype_parm_auto_type : Warning<
"non-type template parameters declared with %0 are incompatible with C++ "
"standards before C++17">,
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -95,6 +95,9 @@
`Issue 57169 <https://github.com/llvm/llvm-project/issues/57169>`_
- Clang configuration files are now read through the virtual file system
rather than the physical one, if these are different.
+- Fix `Issue 57643 <https://github.com/llvm/llvm-project/issues/57643>`_.
+ Missing C++20 compatibility warning of deduced type as non-type template
+ parameters.
Improvements to Clang's diagnostics
Index: clang/test/SemaCXX/template-nontype-args-compat.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/template-nontype-args-compat.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -fsyntax-only -Wpre-c++20-compat -std=c++20 -verify=cpp20 %s
+
+namespace DeducedClass {
+template<class>
+struct DC {};
+
+template<DC s> // cpp20-warning{{non-type template parameters declared with 'DC' are incompatible with C++ standards before C++20}}
+auto test() {}
+} // namespace DeducedClass
Index: clang/lib/Sema/SemaTemplate.cpp
===================================================================
--- clang/lib/Sema/SemaTemplate.cpp
+++ clang/lib/Sema/SemaTemplate.cpp
@@ -1532,9 +1532,17 @@
CheckValidDeclSpecifiers();
if (TInfo->getType()->isUndeducedType()) {
- Diag(D.getIdentifierLoc(),
- diag::warn_cxx14_compat_template_nontype_parm_auto_type)
- << QualType(TInfo->getType()->getContainedAutoType(), 0);
+ if (TInfo->getType()->getContainedAutoType()) {
+ // template<auto xx>
+ Diag(D.getIdentifierLoc(),
+ diag::warn_cxx14_compat_template_nontype_parm_auto_type)
+ << QualType(TInfo->getType()->getContainedAutoType(), 0);
+ } else {
+ // template<DeducedClass dc>
+ Diag(D.getIdentifierLoc(),
+ diag::warn_cxx17_compat_template_nontype_parm_deduced_class)
+ << TInfo->getType();
+ }
}
assert(S->isTemplateParamScope() &&
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -4833,6 +4833,10 @@
"non-type template parameter of type %0 is incompatible with "
"C++ standards before C++20">,
DefaultIgnore, InGroup<CXXPre20Compat>;
+def warn_cxx17_compat_template_nontype_parm_deduced_class : Warning<
+ "non-type template parameters declared with %0 are incompatible with C++ "
+ "standards before C++20">,
+ DefaultIgnore, InGroup<CXXPre20Compat>;
def warn_cxx14_compat_template_nontype_parm_auto_type : Warning<
"non-type template parameters declared with %0 are incompatible with C++ "
"standards before C++17">,
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -95,6 +95,9 @@
`Issue 57169 <https://github.com/llvm/llvm-project/issues/57169>`_
- Clang configuration files are now read through the virtual file system
rather than the physical one, if these are different.
+- Fix `Issue 57643 <https://github.com/llvm/llvm-project/issues/57643>`_.
+ Missing C++20 compatibility warning of deduced type as non-type template
+ parameters.
Improvements to Clang's diagnostics
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